willis



B. D. WILLIS.

TELEPHONE EXCHANGE TRUNKING SYSTEM- APPLICATION FILED JUNE 10. I909. RENEWED on. 29, 1919.

Patented June 1, 1920.

3 SHEETS-SHEET l.

B. D. WILLIS.

TELEPHONE EXCHANGE TRUNKING SYSTEM. APPLICATION FILED JUNE 10, 1909. RENEWED MT. 29, 1919. 1,342,242.

z 9%- g g B. n. WILLIS. TELEPHONE EXCHANGE TRUNKINGSYSTEM. APPLICATION FILED JUNE 10, I909- RENEWED OCT. 29, 1919.

Mm N 4. {BY E L UNITED STATES PATENT OFFICE.

BERNARD D. WILLIS, OF CHICAGO, ILLINOIS, ASSIGNOR- TO AUTOMATIC ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

TELEPHONE-EXCHANGE TRUNKING SYSTEM.

Specification of Letters Patent.

Patented June 1, 1920.

Application filed June 10, 1909, Serial No. 501,272. Renewed October 29, 1919. Serial No. 334,378.

times called a branch exchange, may notonly communicate with each other, but whereby they may also call and be called by the subscribers of an automatic exchange. In such case, andshould a subscriber of the manual exchange call a subscriber of the automatic exchange, the connection is necessarily accomplished through the medlum of the manual switchboard at the branch exchange and the automatic switching apparatus at the main or automatic exchange.

,Also, in systems of this kind occasion often arises for precluding some of the subscribers at the branch exchange from communicating with the subscribers of the main exchange, and vice versa. For example, it is sometimes desirable that one or more of the telephones at the branch exchange be rendered incapable of connection with any of the sub scribers lines at the mainor automatic exchange, but without interfering with the service between any and all'of the subscribers at the branch exchange.

The object of my invention is, therefore, to provide a trunking operators cord circuit of such character that it can be used in trunking to or from some of the suliscribers lines of: the branch exchange, and having provisions wherebyit cannot be used in connection with one or more of the subscribers lines of the branch exchange, thus precluding all possibility of one or more of: the sub scribers of the branch exchange being given trunking connection to or from any of the subscribers of the main or automatic exchange, but without interfering with the establishment of calling connections between any and all of the subscribers of the said branch exchange. Another object is to provide an arrangement whereby the branch exchange is signaled by the transmission of efficiency of a semi-automatic telephone exchange system of this particular character.

To the foregoing and other useful ends my invention consists in matters hereinafter set forth and claimed.

In the accompanying drawings Figure 1 is a diagram of a combined manual and automatic private branch exchange telephone system embodying the principles of my invention, showing an automatic substation A and two manual substationsA and A Fig. 2 represents diagrammatically that part of the central oflice equipment consisting oi the line switch F, master switch H, and the first and second selector switches K and L, respectively.

Fig. 3 represents a connector switch M in which the trunk lines from the second selector (Fig. 2) terminate, and a two-wire substation A connected with an individual line switch F identical in type with the line station. It comprises the usual receiver 2,

switch-hook 3, induction coil 4 which consists of a primary winding 5 and secondary winding (3, transmitter 7, condenser 8, ringer 9 and impulse wheel 10, which latter has the usual impulse teeth 11. The impulse wheel 10 is secured to the shaft 12, to which shaft there is also secured a dial (not shown). When the dial pulled down the springs 14 and 15are not operated, but when the impulse wheel goes back the impulse teeth 11 are adapted to engage the cam 13 upon the end of the spring 14, and thereby carry the latter outv of engagement with the spring 15. Upon the switch hook 3 is secured the earn 16 which, when the switch hook is up, permits the springs 17 and 18 to engage, thereby bridging across the subscribefs line conductors 1 and the primary circuit including the transmitter 7 in series with the primary winding 5. When the switch hooi; is lowered the spring 17 is carried out of engagement with the spring 18 and into ongagement with the spring 21, whereby the ringer t, in series with the condenser 8, is bridged across the line conductors 19 and 20 instead. The manual substation A comprises the usual receiver 22 and switch hook 23 when the receiver is removed, f ed to engage a contact point 2 1-, thereby bridging the ransmitter in series with the n'imary winding across the line. Nhen the receiver is restored to the switch hook the primary circuit through the transmi. and primary winding is broken, and the ringer 20 in series with the condenser 27 's bridged across the line. The line switch I and in: ster switch H (Fig. are of the general pe disclosed in liiiillsll Patent No. 20,301 J06, and in. the ll csiemElectrician oil Chicago, Illinois, of January 11., 18 and 25, 1906. is herein. resented, the line switch i'womp'a'ises a. lun er (not shown) which is attached "he old of a plimger arm, and is adapted when released by the energization the trip magnet 30 to enter a 'roup oi contact springs, forcing the s1 e2, 18, 41c and into engagement With the swings 19, 4:7 and 15, respectively. These springs form the terminal or a trunk line leading to aselector switch h. Each of the line switches F is provided with a number of such groups SPl'll'lgS, each groin l'orming the terminal oi a trunk line leading}; to a separate selector switcl Each trunk line is mu ti plied through the corresponding sprin s in. a number of line switcl s All or the line switches which have access to the same group oi" t 'unk lines are cmitrolled by a common mechanism t switch H in such a manner ti J; the

cup, when not actually in use, are mainne l op iosite an idle trunk line. After a 2 switch plunger has been operated it may turned to normal position. by a spring release mag et 31 i lireen enerd and deinergized. The en --oll relay is provided for dis-sconnectn'ig the trip magnet 39 from the 'ne after the switch has 1 roperated, :1 also when the line to which the switch belongs is called. The master switch ll. conn rises essentially a motor .nagnet tor operating the ratcnet wheel (1, which in turn holds the so-called plunger sl" through the medium of the arm 02. The plunger-s Or the idle line switch normally rest in looking engage ment with the plunge shaft 50, through the medium of which they are maintained opposite idle trunk lines. The master switch also provided with a bank of contacts (3, which bank comprises a common segment (j-il and one individual segment a for each trunk line to which the line switches have access. T he wiper (55 is adapted to always keep the common segment (Set in electrical connection with the individual se 'ment corresponding to the trunk line in front of which their idle plungers are being held. The double-wound relay (S3 is provided for the purpose oi controlling the motor magnet 00.

The first selector ii is form oi the selector switch disclosal in United States Letters Patent No. 815,321, granted ill larch 3,, 1006, to Keith, Erickson and l lricloison, except that the :lorm of release has been changed to that disclosed in United States Erickson. The release is such that as soon as the release magnet energizes, the switch shaft and side switch are restored. l11Sl)i(l 01 having two line relays, as is ordinari the case, this selector provided with one doublewound line relay 91. In addition, the said selector comprises a slowacting lay 92 known as the private magnet relay, and another slow-acting relay 03 known as the releasing relay. The vertical magnet 9 1, the rotary ma gnet 95, the release magnet 96 and the private magnet 97 are ell known and in general operate the same as the magnets of the selector-patent. The said private magnet, of course, controls the side switch wipers 98, 99, 100 and 101. These relays ma be made slow acting in any manner known to the art, for example, by providing each relay with an additional low resistance winding closed upon itself, or by providing each relay with a copper shield, which copper shield is indicated. in the drawings by the small squares at the top of the coil. T

T he second selector ii substantiall the same as the first selector K and is equipped with the same number oi magnets, namely the line relay 102, the private ma net relay 113, the releasing relay 10s, the release magnet 105, the vertical magnet 106, the rotary magnet 10? and the private magnet 108. The circuits, however, are somewhat different and this difference will be taken. up later.

The connector switch 1.41 is a modified form of the connector switch disclosed in Patent No. 815,176 hercinhe'lore referred to. The connecti r switch shalt (not shown), li re the s\ 'itch shaft of the selector, carries the line wipers wiper 111. The connector switch is also controlled by the calling said scriber thro gh the medium of the doulile-wolnnl relay 102) and 110 and the private while the other terminal is connected with the vertical trunk line conductor. The winding 114 is connected with ground and also with the rotary trunk line conductor. This line relay 112 directly controls the vertical magnet 115. The connector switch is provided with the usual rotary magnet 116, and with the slow-acting release relay 117 which is the same as the release relay 104 of the second selector switch. As usual, the private magnet relay 118 controls the private magnet 119, which latter controls the side switch wipers 120, 121, 122, 123 and 124. The back-bridge relay 125,comprising the windings 126 and 127, provides the whereby the terminals of the ringer generator I are intermittently bridged across the normal conductors of the called line. The relay 130 is so arranged thatii a busy line is called, the connector side switch is locked in second position, andthe calling subscriber is given the busy signal. "The means whereby the connector switch may be restored to normal position is provided by the usual release magnet 131 which, when the connector switch shaft is raised one or more steps, is connected to the battery lead by thecontact point 132 and the normal spring 138. By means of the condensers 184 and 135 the circuit or the connector switch is. divided into two sections. The busy signaling apparatus J comprises the interrupter 136 in series with the winding 137 of the Y induction coil 1-38. The winding 139 is connected with the spring 140, and when the relay 130 energizes, the busy signaling apparatus is connectedwith the side switch wiper 120.

The manual stations A and A are each connected with lines which terminate in the jacks C and C respectively, of the private branch, and the automatic substation A is connected with a line which terminates in the jack C. The cord circuit D, which is adapted to connect with the jacks C, C and C is used by the operator to connect a substation of the private branch exchange with an outgoing trunk line to the main central exchange, and is also used by the in-calling subscribers to the private branch exchange.

The cord E is used to connect any two local substations-that is, any two substations vate branch board, such as substations A plug.

and A for example. The cord circuit E is provided with the plugs c and 0 which are adapted to engage the jacks C and C The relays 157 and 158, in connection with the relays 159 and 160, provide means for supplying the substations with battery current for talking purposes. By the use 01 the signal lamps 161 and 162 the operator obtains supervision over the lines corre sponding to the jacks in which the plugs c and 0 are inserted. The condensers 163 and 164 divide the talking circuit into two sections. By means of the key 7' the operator bridges her talking circuit across the calling end of the cord circuit, and by means of the key f a signaling current is sent over the called line.

The cord circuit D is adapted for mak ing calls both ways over the trunk conductors 165 and 166 which connect the main and sub exchan es. The signaling lamp 167 indicates to the operator when the trunk line conductors 165 and 166 have been seized by a calling subscriber at the main automatic exchange, and the lamp 168 acts as a supervisory signal. By means of the key 6 the operator may connect the line terminals of her calling device to the plug 0, or may bridge the generator across the said In this way the subscriber of the private branch exchange may be called or connected with the trunk conductors 165 and 166. Under certain conditions the relay 169 controls the supervisory lamp 168 and the line signal lamp 167.

The operation of the cord circuit E may i be better understood by considering its use for connecting one substation with another. Suppose, for example, that the subscriber at substation A desires to communicate with the subscriber at substation A When the calling subscriber removes the receiver 22 the switch hook 23 engages the contact point 24, thereby establishing an energizing circuit through the line relay 160. Said circuit extends from ground G through the springs 170 and 171, conductor 172, switch hook 23, contact point 24, primary winding 22, transmitter 25, conduct-or 178, relay 160 to the battery lead 174, thence through battery to ground G The relay 160, upon energizing, draws its armature 175 into contact with the contact point 176, thus closing the circuit through the line lamp 177. The circuit through said lamp extends from ground G through the lamp 177, springs 178 and 17 9, armature 175, contact point 176 to the battery lead 174, thence through battery B to ground G In response to the signal the o 'ierator inserts the plug 0' into the jack C, thereby causing the tip 180 and the sleeve 181 of the plug 0 to engage the tip and sleeve springs 171 and 182 and carry them out of engagement with the contact points 170 and 183, respectively.

. hangs up his receiver the circuit there through the arn'iature 1% cents One energizing circuit through the rel y 80 is thereby broken and another circuit established extending from ground it through the relay 158, tip 180 of the plug 0, jack spring 171, over conductor 1'72, through substation A, returning over conductor 173 to the relay 160, through said relay to the battery lead 174:, thence through battery B to ground G. Upon bridging herset across the line by means of the key t the operator learns the." the substatien A is desired. She then inserts the plug into the jack C the causing the tip 18%- and the sleeve 185 of the plug 0 to engt the tip and sleeve springs and 18'? spectively. She then throws the key 7". thereby sending signaling current through the ringer at substation A Upon removing the receiver from the switch hool: the subscriber at substation IL closes the circuit which provides the tran mitter with battery current for talkin purposes. This circuit wXtQlltlS from ground G through the relay 157., eondu t 18a, jack spring 186. conductor r89, threr j substation A conductor 190 tl'u'ough ring spring 187, )lug; sleeve 18S jack 191, conductor 192, relay 159 to the l) lead 1'74, thence tl'irough battery ground The substation is provided with battery current for tal over the circuit which is closed relays 158 and 1.60 when the plug 0 serted in the jack C, which circuit has already been traced. Furtherniore at the time when the plug 0 is inserted in the C a circuit is closed through the re and 160. This circuit extends 5;; G through relay 1%, conductor 195, SlQQ'rQ 181, jack spring 182 through the relay 160 battery lead 174-, thence through lettcry to ground G The relay 194-, on ener 1. closes a circuit through the supervisory a 161. This circuit extends from through the supervisory lamp 161 point 198, armature 199 to the battery lead 1741:, thence through battery l3 g ound G.

As soon as the called subscril er at i A answers, the energizing circuit the relay 153? pulls up the armature breaking a circuit through the s lamp 1G1. thereoy indica in to the that the call has been ans vcred.

' vVhe-n the subscriber at substation relay 15 7 is broken allowing the 198 to fall be it and again through the lamp 161.

lVhen the subscriber at substation IL hangs up his receiver the circuit through the relay 158 is broken, and the all ature 2U lalls baclr into contact with the contact point 203., thereby closing the circuit through the lamp 16 The operator, seeing both lain lighted, knows that the conversation has been completed. and proceeds to withdraw the plugs 0 and 0 Suppose that the subscriber at substation A" desires connection with the substation A. In that case the plug 0 will be inserted in the jack C and the subscriber at substation it called in the regular manner. hen the I'Q'CoiVGl :2 is then removed from the switch heel; 8 circuit is closed through the relays if)? and 202, and the two substations A and are connected in a manner similar to that previously explained. Of course, should subscriber at substation A desire conion with the subscriber at substation A he enioves his receiver from the hook ,clos

g the springs 17 and 18, a d thereby com- 1 it ing an energizing circuit tln'ough the signal relay 202. In this case the plug 0 will be inserted in the jack 0 and the plug 0 into the jack C. In a similar manner subscriber A can call subscriber A, or subscriber A can call subscriber A tiunuose that the subscriber at substation to call the subscriber at substaion A which is a substation at the central e-" :lia1i;;e. Upon learning that the substan it", the calling number oi? which, for nple may be taken as 2220 is wanted operator removes the plug 0 from the act; C and substitutes the plug (1 of the trunk c 'cuit D. She then throws the key 6, thus bridging her calling device N cross the line. As soon as this is done a circuit is closed through the said calling 1 said circuit extending from ground 2), through the trip magnet 9 l.l lf :6-(5lit-Oif springs 5"? and 56, contor E503, rotary line conductor 166, ouch the springs 204; an-ril 205 conductor 2306, the cperetofis calling device 1?, e011- durt r .n "1 prings 208 and 205), conductor l), springs 211 and 212, vertical. line coni 165 through. the luridge-cut-oli and 59, re stance 181 to the 111% thence th ou'l h battery B :i. The trip in 80, upon g attracts its arrn l 341.. causplunger 28 to be driven into the i jacl; u As soon as the plunger 28 F1" ters the Salli bank jacl" .it operates to press a be; h springs l? d ll '15) and 48, t3 3 ab. and 43:5 and I l: into contact. The springs 4:53 and 4t? completes one: Zing circuit tl'irough the bridgecm oil relay This circuit ext nds from and (1 through the springs 41': and 4:7, uctor 1G7" ,hrough the relay to the lead 110, thence tln'ough battery B 1 ground (In The cut-oil relay then aerates the cut-off relay sprii 1 breaking the originally establish cir uit through the rip Ina The clcs'ne of contact between the nanlci spz'in 1 43 extends the subscribers vertical line conductor 165 into contact with the trunk conductor 82,

and the making of contact between the bank the winding 215 of the relay 91, contact point 216, side switch wiper 99, trunk conductor 83, bank springs and 14;, conductor 166, thence through the calling device N to the vertical line conductor 165, through the bank springs 42 and 43 to the trunk conductor-82, thence through the side switch wiper 98, contact point 217, winding 218 of the line relay 91 to the battery lead 110, thence through battery B to ground G. The closing ofthis circuit causes the line relay 91 to energize, the windings 215 and 218 being in series, and operates to separate the springs 219 and 220, placing the spring 220 into contact with the spring 221. In consequence the slow-acting release relay 93 is energized and in turn operates to shift the spring 222, which is connected with the spring 223, out of engagement with said spring and into engagement with the spring 224. The energizing circuit for the relay 93 extends from ground G to springs 220 and 221, through said relay 93 to the battery lead 110, thence through battery B to ground G. By slmv-acting relay is meant relays. that are slow only in deenergizing. By the energization of the relay 93, as described, it will be seen that the spring 219 a is placed in contact with the slow-acting private magnet relay 92, and through said relay to the vertical magnet 94,,making it possible to send ground impulses from the spring229 through said magnet 92 tothe vertical magnet 94: while the relay 93 is energized. i I

The foregoing is accomplished by the operator when she bridges her calling device across the line. She continues the call by breakingvsaid circuit in any suitable manner a number of times, corresponding to the 7 units in the first digit. It will be assumed 50 that her calling device is equipped with the regular dial. When, therefore, the dial is drawn down for the said first digit 2, on returning to its normal position it operates to twice break the established circuit just .described. Each time that this circuit is broken the line relay 91 of the selector K falls back and permits the spring 220 to come into contact with the spring 219, and

impulses are transmitted from ground G at K (Fig. 2) byway of the springs 220 and 219 of the line relay and the springs 222 and 224- of the slow-acting release. relay 93 through the private ma net relay 92, the vertical ma 'net 94, side switch contact point 225, wiper 101 to the battery lead 110,

a the vertical magnet 9 1, which magnet then thence through battery 13 to ground G. It is, of course, understood that the impulses are so regulated that the slow-acting relay 93 does not have time to de'energize between impulses, The first impulses transmitted by the line relay 91 over the circuit described causes the private magnet relay 92 to energize, and said relay remains so during the operates to raise the switch shaft one step for each impulse. Since two impulses are transmitted to the shaft the lineand .private wipers 88, 89 and 90 are raised two steps and brought opposite the first con-. tacts of the second bank level of the selector K. As soon as the operators dial assumes its normal position the line relay 91again resumes its constant energized condition, so that the private magnet relay 92 deenergizes, whereby the springs 226 and 227 are allowed to separate and the private magnet 97 as a result allowed to de'energize, whichthen allows the side switch to shift to second'position. As soon asthe side switch shifts to second position the side switch wiper 101 engages the contact point 228, thereby es tablishing an energizing circuit through the rotary magnet 95, said circuit ,CXtQDCllIIg from ground G through the interrupter springs 229, through the rotary magnet side switch wiper 101 to the battery lead 110, and through battery B to ground G.

The rotary magnet then attracts its armature, rotating the shaft one step and thus causing the line wipers to come into contact with the first trunk line in the second level. When the rotary magnet 95 attracts its armature the armature of the private mag- 1 5 net 97 is operated at the same time by the usual privatearmature finger carried by the rotary armature. The result is that the first operation of the rotary magnet not only rotates the shaft'wipers into engagement with the first trunk line, but as the rotary armature falls back the private armature is also permittedto fallback, at which time the side switch shifts to third position. This is ,onlyitrue if the first trunk is: idle, which trunk, it is assumed, terminates in a secondselector'L. It will be seen that when the side switch passes to third position the side switch wiper 100 engages the contact point 230, whereby the private wiper 90 is placed in connection with ground (i since the line relay 91 is energized. The circuit over which this connection is maintained is as follows: from ground G through the line relay springs 220 and 221, conductor 231 to the contact point 230, thence to the side switch wiper 100 and over the conductor 232 to the private wiper 90. The private wiper being in engagement with one of the multiple private bank contacts corresponding to the trunk line terminating in the selector L, all of the multiple private bank contacts connected thereto are thus provided with a guarding potential for preventing other selectors from seizing the same trunlr line If the first trunk line is busy, however, the armature of the private magnet does not fall back with the rota." r armature at the end of the first step, but is retained by the private magnet, which is then energized over a circuit which is closed as sooi'i as the private wiper engages the first coin tact, which will, of course, be grounded. Then this happens an energizing cirruit is set up through the private magnet 9'? extending from this grounded private bank contact to the wiper 90, over the conductor 232 to the side switch wiper 100, thence to the contact point 233, through the private magnet 97 to the battery lead 110, thence through battery B to ground It will be seen, therefore, that the private magnet 90 will retain the side switch locked in second position as long as the private wiper 90 encounters busy trunk lines. However, as soon as the rotary magnet 95 advances the wipers onto an idle trunk line, the energizing circuit for the private magnet 97, including the private wiper 90, is broken, and as a result the private magnet 97 will deenergize at the last stroke of the rotary magnet, permitting the side switch to pass to third position. A guarding potential .is then established at the private wiper 90, and then over the private bani: multiple contacts, as already explained.

It will be assumed that the first selector K stops on the first trunk line, as previously explained. Then when the side switch passes to third position the side switch wipers 98 and 99, upon engaging the thirdposition contacts 234; and 235, respectively, extend the trunk conductors 82 and. 83 to the trunk conductors 2 15 and 2 1%. which terminate in the second selector L. It is evident that when the side switch of the first selector is in first position the wipers 98, 99, 100 and 101 are in engagement with the contact points 217, 216, 238 and 225., respectively; when in second position the wipers are in engagement with the con act points 289, 240, 233 and 228; and in third position the wipers are in engagement with the contact points 234;, 235, 280 and 241. It will be seen that when the side switch thus passes to third position the energizing circuit tor the line relay 91. of the selector ii is cut oil from the said relay, which restores to nor mal. The energizing circuit for the line relay 91 cannot be broken until the said side switch passes to third position, because the side switch contact points 21? and 239 are connected. on one side, and the side switch contact points 210 and 210 are likewise connected on the other side. lVhen the connection with the ground G is interrupted at a point between the line relay springs 220 and 221 a. guarding potential is established at the private bank contact engaged by the private wiper 90 from the selel'jztor L as follows: As soon as the side switch trips to third position the line relay 102, like the line relay 91, energizes over the following circuit: from ground. G through the winding 2 12 of the relay 102, side switch wiper 2 13 of the second selector L, thence through the trunk conductor 241 .1, rotary line wiper 89 of the first selector K, contact point 235, side switch wiper 99, through the calling device N, back over the other side of the line to the first selector si ie switch 98, contact point 234%, vertical line wiper 18 to the side switch wiper 246 of the second selector L, thence through the winding 24:7 of the line relay 102 to the battery lead 110. thence through battery B to ground G. The line relay 102 being similar to the line relay 91, the spring 2 18 is separated from the spring 249 and carried into contact with the spring 250. As a result the slow-acting release relay 10% is energized by a flow of current from ground G throi'igh the spring 248 and 250, release relay 104: to the battery lead 110., thence through battery P to ground G. The slow-acting relay 10 1, upon energizing, shifts the spring 251 "from the spring 252 and into contact with the spring 253, and the two additional springs and are pressed into contact at the same time, whereby the ground coiiincction G is substituted at the private viper 90 for ground (W. This is evident, since the side switch of the selector L is in first position, and is also true when the side switch is in second position, as indicated by the side switch contact points 257 and. 256 being connected.

Connection having been established with the second. selector L, the operator pulls the dial in accordance with the second digit 2, with the result that the line relay 102 is operated twice and the spring 248 carried twice into engagement with the spring 2 19, while the slow-acting relay 104; is energized. The result is that at the 1 st impulse the slow-acting private magnet relay 103 is energized, and the vertical magnet 106 operated once. The slowacting relay 103, of course, remains energized until the second impulse is sent, which again operates the vertical magnet 106 through the slow-acting relay 103.

by the vertical magnet 106, and the line and private wipers 258, 259 and'260 are "placed opposite the first contact of the seeond level of the second selector bank. will be evident that as soon as the slowac'ting relay 103 energizes, the springs'261 and 262 are pressed into contact and an energizing circuit is established for the private magnet 108 from ground G through the springs 261 and 262, through the private magnet 108 to the battery lead 110, thence through battery 13 to ground G. The private magnet attracts its armature, but does not release the side switch to second position until all of theinipulses have been sen'tyin, after which the slow-acting relay 103 deene'rgizes, as in the first selector K, which then interrupts the circuit between the springs 261 and 262. The energizing circuit for the'vertical magnet 106 and for the slow-acting relay 103 extends from ground G through'the line relay spriiigs 2418 and 2419, through the relay springs 251 and 253 to the private iiiagnet relay 103, thence to the vertical magnet 106, side switch point 263, side switch wiper 26s to the battery lead 110, thence through battery 13 to ground G, When the side switch passes to second position the side switch wiper 26 1 engages the contact point 265, thus closing the energizingcircuit for the rotary magnet 107 from ground Gr to the interrupter Q springs 266, rotary magnet 107, side switch contact point 26:3,s1d'e switch wiper 264% to the battery lead 110, thence through battery B to ground G. It will be seen that 'in the selector L, as in the selector K, at

the first impulse through the rotary magnet 107 the armature Oftlle private magnet 108 is operated to trip the side switch to third position, provided the first trunk line is idle, by which operation the subscribci"s lineis placed in connection with the con- .nector switch M. However, if the first trunk line is not idle, theprivate wiper 260will be carried onto grounded contacts, as de rotated into engagement with the trunk conductors 268, 269 and 270, and the side switch wipers 2 i6and 2 13 having passed to third position,the circuit is thereby extended to the connector switch M. The connector line relay 112 instantly energizes, the current flowing from-ground G through the trunk conductor 269, rotary line wiper 2539 0]? the second selector L, contact point 27 3, side switch wiper 243 to the rotary side of the line, through the first selector K, line switch F, calling device N to the vertical side of the line, back through the line switch F, first selector K and the second selector L to the side switch wiper 246, contact point 272,11116 wiper 258, vertical trunk conductor 268, winding 113 of the line relay 112 to the battery lead 110, thence through battery B to ground G. The line relay 112, upon energizing, operates to shift the spring 273 from the spring 274; to the spring 275, whereby an energizing circuit is established through the release relay 117, said circuit extending from ground G" through the springs 273 and 275, relay 117 to the battery lead 110, thence through battery B to ground G. Vhen the relay 117 energizes, the spring 276 is shifted out of contact with the spring 277 and into contact with the spring 278, and'the spring 279 is shifted into engagement with the spring 280. This primary operation of the connector relays 1.12 and 117 occurs at the instant that the side switch wipers 246 and 243 of the selector L pass to third position,

i and extends the subscribers line conductors to the connector M. The en a ement of the springs 280 and 27 9 establishes a guarding when the side switch of the second selector- L passes to third position a new energizing circuit is established through the release relay 104;, said circuit extending from ground G at the connector switch through the side switch wiper 123 and springs 279 and 280 to the conductor 270, through the shaft wiper 260, side switch wiper 271, conductor 281, through the release relay 104 to the battery lead 110, thence through battery B to ground G. Also, this'same guarding potential established at the contact engaged by the private shaft wiper 260 is extended to the'private bank contact engaged by the shaft wiper 90 of the first selector K. When the side switch of the second selector L passes to third position the path over which this potential extends is the same as just traced to the side switch wiper 271, from whence it goes to theshaft wiper 90. The

operation of the dial for the last two digits affects the connector switch, and When the dial is operated for the third digit 2 the circuit through the line relay is twice broken, thereby momentarily deenergizing said relay twice, whereby thespring 273 the winding 114- of the line relay 112 to i Cir twice engages the spring 27 1-, thus sent ling" two impulses to the vertical magnet 115 from ground G through the springs 278 and 274;, springs 276 and 278, through the vertical magnet 115, contact point 282, side switch wiper 12a, private magnet relay 1.18 to the battery lead 110, thence through battery to-ground The prhite magnet relay 118 energizes when the impulse delivered, and since the said relay is slowacting it remains in an operated position until all. of he vertical impulses are sent. The vertical magnet, upon being energized twice, operates to carry the shaft wipers 109, 110 and 111 two steps to a point opposite the second level. The relay 118, upon energizing, shifts the spring 288 out of engagement with the spring 2841 and into engagement with the spring Also, the spring 286 is shifted out of engagement with the spring 285. When the spri] 288 and 285 engage, energizing circuit is established through the private mag et .19 from ground il through the springs 285 and 288, private magnet 119 to the ba tery lead 110, thence through battery ll to ground (in V The relay 118, being a slow-acting relay, remains in an operated position while the vertical impulses are being sent; but alter all of the impulses are delivered, and the line relay 112 returns to its operated position, the circuit through the relay 118 becomes broken, thus permitting the sprmgs 286 and 288 to return to normal position. \Vhen the springs 288 and 285 disengage, the circuit through the private magnet 119 breaks, whereby the said magnet deenergizes, permitting the side switch to pass from first to second position. The operator now pulls the dial for the last digit O, thereby transmitting ten impulses, and operating the line relay 112 ten times. Each time that the line relay springs 278 and 27 1 engage, an energizing circuit is established through the rotary magnet 116 from ground G through the said springs 278 and 27 1, through the springs 276 and 278, locking relay springs 287 and 288, through the rotary magnet 116 to the contact point 289, thence through the side switch wiper 12st, through the pri vate magnet 118 to the battery lead 110, thence through battery B to ground .G. Again the private magnet relay energizes, as in the previous case, remaining so until all of the impulses are transmitted, thereby retaining the private magnet energized. The rotary magnet 116 thus operates to rotate the shaft wipers into engagement with the desired line #2220. As soon as the line relay 112 ceases to operate for the last digit, the private magnet relay 118 deenergizes, as hereinbetorc explained, in this instance permitting the side switch to trip to third position. The result is that the side switch.

wipers 120, 121, 122, 128 and 12d engage the contact points 290, 291, 292, 298 and 2941, respectively. WVhen the side switch wiper 122 engages the contact point 292 a guarding potential is completed at the private wiper 111 for protecting the seized line from outside interference while the connection is established. This guarding potential extends from ground G to the contact point 292, thence by way of the side switch wiper 122, locking relay springs 295 and 296 to the private wiper 111. Not only does this guarding potential protect other connectors 'irom seizing the same line over multiples of the normal conductors 297, 298 and 299, but it also provides means for energizing the cutoil relay 800 at the line switch F, whereby the switch F is prevented from operating when the called subscriber removes his receiver 801 from the switch hook 802. l/Vhile the side switch is in first or second position a guarding potential is established for the trunk conductor 270 at ground 9' through the side switch wiper 128. The reason for this is that the guarding potential from the ground G is interrupted while the line relay 112 is operating, and there is a possi hility some other selector similar to the second selector L stopping on the same trunk line. After the side switch passes to third position, however, there is no such possibility, and the potential is provided by ground G through the line relay springs instead. When the side switch wipers 120 and .121 engage their third-position contact points 290 and 291 the trunk conductors 165 and 186 are placed in connection with the called subscribers line over the heavy conductors shown, passing through the ringer relay springs 808 and 80 1 on one side and 805 and 806 on the other. As soon as con nection is thus established the ringer relay 129 is energized over the circuit established when the side switch wiper 124i engages the contact point 291, the energizing current a lowing from ground G through the interrupter 128, through the back-bridge relay springs 808 and 309, ringer relay 1129, conductor 810, contact point 29 1, side switch wiper 124, private magnet relay 118 to the battery lead 110, thence through battery B to ground G. It will be seen that as the interrupter 128 revolves, the energizing circuit of the ringer relay 129 will be broken periodically, so as not to ring the called subscriber continuously. Each time that the ringer relay is energized the springs 808 and 805 are separated from the ringer relay springs 80% and 306, thereby separating the called line from the calling line and pressing the springs 803 and 805 into contact with the springs 811 and 812, which latter are the terminals of the ringer generator As a result ringing current is sent over the called. line for energizing the bell 813,

while the springs. 314 and 315 are in contact. As soon -,as the called subscriber answers, the back-bridge relay 125 is energized by a flow of current from ground G contact point 292, side switch wiper 122, winding 127 of the back-bridge relay 125, conductor 316, ringer relay springs 306 and 305, side switch wiper 121, contact point 291, rotary line wiper 110 rotary normal conductor 298, rotary line conductor 317, switch hook springs 315 and 318, impulse springs 319 and 320, transmitter 321, vertical line conductor 322, vertical normal conductor 297, Vertical line wiper 109, cont-act point 290, side switch wiper 120, ringer relay springs 303 and 304, conductor 323, winding 126 of the back-bridge relay 125, thence to the battery lead 110, and through battery B to ground G. When the back-bridge relay 125 is energized the energizing circuit for the ringer relay 129 isrinterrupted at a point between the springs 308 and 309, keeping the ringer relay deenergized as long as the called subscriber is on the line.

The operator, having obtained the called subscriber, restores the key (2, thereby connecting the substation A directly with the trunk line conductors 165 and 166, since the sleeve contact 20S of the plug C engages the sleeve 191. which is connected with the main battery 13 through the relay 159. An energizing circuit therefore extends from ground (1 through the relay 169 (Wer the sleeve contact 208 ring 191 to the relay 159, thence to battery lead 174, and through battery 13 to ground G When the relay 169 energizes and pulls the armature 209 into contact with the contact point 210 the station A connected with the trunk conductors 165 and 166, as shown, over the heavy line conductors of the cord circuit D. The operator, throwing her listening key 6, informs the subscriber at substation A that the connection has been completed.

The trunk conductors are extended through station A over the following circuit: Starting with the conductor 165 the circuit extends through the springs 212 and 324, springs 325 and 326, through the tip of the plug C, jack spring 186, conductor 189, through the station A conductor 190, jack spring 187,sleeve of the plug 0, through the springs 329 and 330, contact point 210, armature 209. through the winding 333 of the relay 334 through the armature 335, contact point 336, conductor 337, through the springs 327 and 204 to the trunk conductor 166. I \Vhen the relay 169 is energized the armatures 335 and 338 are brought into contact with the contact points 336 and 339,

r spectively. This closes a circuit through the lamp 168 as long as the key 0 is thrown after plugging in the plug c, said circuit extending from ground G through the armature 333, conductor 340, armature 341,

contact point342, lamp 168 to the main battery B thence through battery B to ground G As soon as the key 0 is returned, and the connection completed, the circuit through the lamp 168 is broken at the contact point 342 by the energization of the relay 334 through the winding 333, as before stated. 7

After the subscribers are through talking, if the calling subscriber hangs up his receiver he opens the line circuit at a point between the springs correspondingto the springs 23 ,and 24 at the substation A, thereby deenergizing the relays of all of the switches as follows: At the instant that the circuit is broken between the said springs 23 and 24 the double-wound linerelay 112 and the release relay 117 of the connector M deenergize. slow-acting relay 117 and the line relay 11.2 deenergize, the energizing circuit for the release magnet 131 is closed at a point between the springs 276 and 277, and at another point between the springs 274 and 273. The flow of current is, therefore, sent from ground G through the springs 274 and 273, throughthe springs 276 and 277, the release magnet 131, thence through said magnet to the off-normal spring 133, contact point 132 to the battery lead 110, thence through battery B to ground G. The release magnet instantly relcases the connec tor switch shaft and side switch, thereby breaking the energizing circuit through the back-bridge relay 125 if the called subscriber has not in the meantime restored his receiver, and also the energizing circuit through the bridge-cutoff relay300 of the called line switchF. As soon as the connector switch shaft reaches its lowest position it breaks acircuit for the release magnet 131 by separating the off-normal spring 133 from the contact point 132, at which instant the release magnet of the connector isv also restored. The operation of the line relay 112 and ofthe slow-acting relay 117 not only causes the release of the connector, as described, but also the release of the succeeding circuits, becausethe ground connection from ground G" to the trunk-release conductor 270 is interrupted by both of these relays. Since the release relays 104 and 93 are dependent upon that ground for At the moment that the their energized condition, it follows that they willfall back, withthe following result; As soon as the releaserelay 104 of the second selector L deenergizes, the spring 251 falls back into normal engagement with.

the spring 252, thereby closing an energizing circuit for the release magnet 105 from ground (al through the springs 248 and 249, through the springs 25]. and 252, the release magnet 105, thence to the contact point 343, oif-normal spring 344 to the battery lead 110, thence through battery B to the call by operating his own dial.

ground G. As soon as the release magnet 105 energizes, the second selector side switch and switch sha'lt't are restored, which latter, upon reaching its lowest position, opens up a release circuit at a point between the oilnormal spring 344 and the contact point 343, whereby the release magnet 105 is also restored. lVhen the release relay 93 of the selector K deenergizes, the springs and are brought into contact and as a result the energizing circuit for the release mag net 96 is closed. The energizing current for this release magnet 96 flows from ground G to the springs 220 and 219, through said springs 223 and 222 to the release magnet 96, thence through said 1nagnet to the contact point 3&5, oil-normal spring 346 to the battery lead llO, thence through battery B to ground G. The release magnet, upon energizing, then restores the first selector side switch and switch shaft, which latter, upon falling into position, opens an energizing circuit for the release magnet 96 at a point between the off-normal spring 846 and the contact point 34:5. lVhen the magnet 96 energizes a circuit is closed through the release magnet 31 ot the line switch F, said circuit extending from ground G through the springs 3%? and 348, conductor 8%, bank contacts as and t8, release magnet ill to the battery lead 110, thence through battery ll to ground (1. hen the circuit through the relay 96 is broken by the separation of the off-normal springs 845 and 346 the springs 34;? and 348 separate, breaking the energizing circuit through the release magnet 31, thus allowing the armature to fall back and withdraw the plunger from the bank. The system is then restored to normal and made ready for another call.

Should the subscriber at substation A desire to call the main exchange, the operator inserts th plug 0 into the jack C, thereby connecting him through the trunk D in the same manner that station it? was con nected. i being an automatic substation the subscriber then proceeds to complete Upon releasing in this instance, as in the preceding, the circuit through the relay an is broken, allowing the armature 841 to return into contact with the contact point 341-2, and thus closing the circuit through the lamp 168 from ground (i through the relay armature 338, conductor 34M), armature 341, contact point 3452, lamp 168 to main battery. The glowing of this lamp then indicates to the operator that the trunk D has been vacated. When the trunk D is seized by a subscriber from a main exchange the operator at the private branch Xchange is signaled by the subscriber throwing generator on the line. hen this is done at current is sent over the line '16:) through the neaaeaa springs 212 and 82 i, conductor 3-19, contact point 350, armature 335, conductor 351, winding 333 of the relay 334, armature 209 through the condenser 352, and back over the trunk line 166 to the other side of the generator. The relay an energizes,pulls up the armature 3M and establishes an energizing circuit through the windings oil? the relay 334, and also to the lamp 167, over the following path: from ground G to the contact point 354, through armature Ml, conductor 340, armature 2338, contact point conductor 356, springs 357 and 2358, conductor 359, and from thence through the winding 353 of the relay 33st on one hand, and the lamp 167 on the other, to the battery B thence through battery B to ground i. The relay :El-tconsequently locks and maintains the circuit through the lamp 167, which calls the operators attention. The operator, throwing her listening key 6, learns what substation of the private branch exchange is desired, and inserting the plug 0 into the jack of the desired line throws the generator key 0, which sends out generator current to the station called.

In calling out over the trunk D the operamanner, in order to maintain the connector up in case the receiver at the calling station should be on the hook when the key 0 is restored. lVhen the key a is thrown a circuit is closed extending from ground G to con tact point 339, armature 838, conductor 34:0, armature 34:1, contact point 34-2 to the springs 361 and 862, relay 363 to the battery lead thence through battery B to ground G This relay attracts the armature 364- and completes a locking circuit through itself from ground G contact point 339, armature 338, conductor 3&0 to armature 341, contact point 342, armature 3651-, contact point 365, through relay 363 to battery lead ll thence through battery B to ground (2 At the same time that the ari'nature 361 is attracted the armature 366 is likewise attracted against the point 867. This bridges the resistance 360 between the springs 324i and 327. It the receiver is on the hook at the calling substation when the operator throws back the key 0', the resistance 360 will be bridged across the trunk conductors 165 and 166 by the engageinei'it ot' the springs 324 and 327 with the sprin s 312 and 204, respectivelf-J. As soon, however, as the receiver at the calling substation is removed from the hook theenergizing circuit of the winding 333 of the relay 334i is completed, as previously stated, YVllOlGlllfiOll the locking circuit ol" the relay 363 is opened at a point between the armature 34:1 and contact 342. 'llhe relay 363 then deenergizes and opens the bridge through the resistance 800. i

I exchange.

If, however, a subscriber at substation A attempts to call the main exchange, it will be found impossible to make the connection. 'lheoperator. on learning that a. trunk to ;the main exchange is desired, may insert the-plug 0 into the jack C. When this is they cannot call a substation of themain exchange.

From the foregoing it will be seen that I provide a trunking operators cord circuit which is rendered operative by the insertion "of the plug in the jack of one or more of the lines at the branch exchange, but which is rendered or retained in an inoperative condition when an attempt is made to use the same for connection with one or more other lines of the same exchange. Thus, some of" the subscribers can call and be called by the subscribers of the main exchange, whereas other subscribers of the branch exchange have their service limited entirely to intercommunication between the subscribers of the branch exchange, inasmuch as they are entirely cut off from service to or from the main exchange. This would be desirable, for example, in a system involving a branch exchange requiring a considerable number of substations for local communication, but only a part of which substations in the ordinary transaction of business have occasion to be connected With substations of the main With this system employees of an institution who ordinarily have no occasion to call outside subscribers may be given a telephone for local communication, but will be unable to monopolize the trunks to the main exchange for personal and unimportant matters. Moreover, it will be seen that when the operator at the branch exchange is called by a subscriberat the main exchange, the trunk line signal at the trunking operators cord circuit responds to the regular ringing current which passes over the trunk line from the main exchange. Again, the trunking connection which has been automatically extended to the called subscribers line at the main exchangeis not released if the trunking operator restores the falling key when the calling subscribers telephone is hung up in normal condition.

What I claim as my invention is 1. In a telephone system,a trunking operators cord circuit terminating at one end in a plug and at'the other end in an automatic switch, a subscribers'line provided with means for rendering said cord circuit operative for talking purposes when connection is madethereto, and another subscribers line provided with means for rendering said cord circuit inoperative for talking purposes when connection is made thereto.

2. In a telephone system, a trunking operators cord circuit provided with a normally open. talking strand, a relay controlling said normally open strand, a sub scribers line provided with means for energizing said relay to close the talking strand, and another subscribers line provided with means for causing said relay to remain in normal condition.

Ina telephone system, a branch exchange and a main exchange, a trunk extending between the two exchanges, a cord and plug at the branch exchange permanently connected to said trunk, a plurality of subscribers lines each provided with a jack adapted to'receive said plug, circuit means at the jack of one of said lines for rendering said cord circuit operative for talking purposes, and circuit means at the jack of another of said lines for rendering said cord circuit inoperative for talking purposes.

4. In a telephone exchange system, a subscribers line, a trunk line adapted to be connected thereto, automatic means for extending connection therefrom, including an operators calling key and automatic switches adapted. to be released by opening the line circuit, and circuit means whereby the automatic connection is not released should the operator restore the calling key while calling subscribers telephone is hung up or in normal condition.

5. In a telephone system, a calling line, a trunk line, means for establishing a connection therebetween, automatic means for ex-- tending connection therefrom, including an operators calling key and automatic switches adapted to be released by opening the line circuit, and a suitable resistance adapted to be bridged across the trunk line, whereby'the automatic connection is not released should the operator restore the calling key while the calling subscribers telephone is hung up or in normal condition.

6. In a telephone system, a trunking operators cord circuit, asubscribers line prothereto, and electrically controlled means for calling and releasing automatically over circuits each of which includes a portion of one side of the talking circuit in series with a portion of the other side thereof. y

7. In a? telephone system, aJtrunking operators cord circuit provided with a normally open talking strand, a relay controlling said normally open strand, a suln scribers line provided with means for energizing said relay to close the talking strand, another subscribers line provided with means for causing said relay to remain in normal condition, and electrically con trolled means for calling and releasing auomatically over circuits each o'l' which includes portion of one side of the talking circuit in series with a portion of the other side thereof.

8. ln a telephone exchange system, a subscribers line, a trunk line adapted to be connected thereto, automatic means for extending connection therefrom, including a operators calling key, circuit means whereby the automatic connection is not released should the operator restore the calling key while the calling subscribers telephone is hung up or in normal condition, and elec trically controlled means for calling and releasing automatically over circuits each of which includes a portion of one side of the talking circuit in series with av portion of the other side thereof.

9. In a telephone system, a subscrihers line, a trunk line adapted to be connected thereto, automatic means for extending connection therefrom, including an operators calling key, a suitable resistance whereby the a utomatic connection is not re leased should the operator restore the calling key while the calling subscriber s telephone is hung up or in normal condition, and electrically controlled means for calling and releasing automatically over eircults each of which includes a portion of one side of the talking circuit in series with aportion of the other side thereof.

10. In a telephone system, a trunking operators cord circuit terminating at one end in a plug and at the other end in an automatic switch, a subscribers line provided, with means for rendering said cord circuit operative for talking purposes when con nection is made thereto, :uiother subscribefis line provided with means for rendering said cord circuit inoperative for talking purposes when connection is made thereto, and a common battery for supplying Cllll'GDt for talking purposes.

11. In a telephone exchange system, a sub scribers line, a trunk line adapted to be connected thereto, automatic means for extending connection therefrom, including an operators calling key, and automatic switches adapted to be released by opening the line circuit, circuit means whereby the automatic connection is not released should the operator restore the calling key while the calling subscribers telephone is hung up or in normal condition, and a common battery for supplying current for talking purposes.

insane-e 12. In a telephone system, a subscriber s line, a trunk line adapted to be connected therewith, automatic means for extending coi'inection thcretron'i, including an operators calling key and automatic switches adapted to be released by opening the line circuit, a suitable resistance adapted to be brought into suitable relationship with the trunk line, whereby the automatic connection is not released should the operator rcstore the calling key while the calling subscribers telephone is luing up or in normal condition, and a common battery tor supplying current for talking purposes.

13. in a telephone systen'i, subscribers lines, an operatofs cord circuit adapted to be connected with said lines, a relay for said cord cir .lllli, an operatofis key adapted when operated to close an energizing circuit. for said relay, a suitable resistance adapted to be bridged across the cord circuit by the ope a llOll of said relay, and locking means for said relay whereby said bridge is maintained closed after said key is released.

ll. In a. telephone system, siIbscrilmrs lines, a trunk, a tri'inking operato cord circuit connected with said trunk and adapted for use in establishing a connectnm either to or from said trunk, a relay for said cord circuit, and a trunk signal and a supervisory signal both under thecontri'il of said relay.

15. Tu a telephoi'ie system, a group oi? lines, a trunk, another group o'l? lines, circuit closing means for extending coi'inection to said trunk from any one of said lines, said trunk being normally inoperative for extei'iding a circuit thereover, whereby when connection is extended to said trunk from said first group of lines the connection cannot be extended beyond said trunk, electrically controlled means for rendering said trunk circuit operative, and auxiliary circuits associated with said second group of lines for controlling said electrically controlled means whercby when any connection is extended from any one o'l said lines of the second group to the said trunk the trunk becomes operative to extend a connection. th GI'GYFI'OD].

16. In a telephone system, a group of lines, a cord circuit, another group of line circuit closing means for extending connection to said cord circuit from any one of said lines, said cord circuit being normally inoperative for extending a circuit 'thcreover, whereby when connection is extendei'l to said cord circuit from said first group of lines the connection cannot be extended beyond said cord circuit, electrically controlled means or rendering said cord circuit operative, auxiliary circuits associated with said second group of lines for controlling said electrically controlled means whereby when any connection is extended from anyone of said cally controlled means for rendering said trunk circuit operative, auxiliary circuits associated with said second group of lines for controlling said electrically controlled means whereby when any connection is extended from any one of said lines of the second group to the said trunk the trunk becomes operative to extend a connection therefrom, and a central battery for operating and talking purposes.

18. In a telephone system, a trunk line normally inoperative whereby when a certain line is connected therewith calls are prevented from passing over said trunk, another line, an auxiliary circuit associated therewith for rendering said. trunk operative whereby calls may be transmitted over said trunk, and electrically controlled operating means for calling and releasing automatically, said means controlled over a portion of one side of the talking circuit in series with a portion of the other side.

19. In a telephone system, a group of lines,

a trunk, another group of lines, circuit clos-- ing means for extending connection to said trunk from any one of said lines, said trunk being normally inoperative for extending a circuit thereover whereby when connection is extended to said trunk from said first grpup of lines the connection cannot be extended beyond said trunk, electrically controlled means for rendering said trunk circuit operative, auxiliary circuits associated with said second group of lines for controlling said electrically controlled means whereby when any connection is extended from any one of said lines of the second group to the said trunk the trunk becomes operative to extend a connection therefrom, and electrically controlled means for calling and releasing, said means. controlled over a portion of one side of the talking circuit in series with a portion of the other side.

20. In a telephone system, a trunk line normally inoperative whereby when a certain line is connected therewith calls are prevented from passing over said trunk, another line, an auxiliary circuit associated therewith for rendering said trunk operative whereby calls may be transmitted over said trunk, and a central battery for supplying current for talking and operating purposes.

Signed by me at Chicago, Cook county, Illinois, this 3 day of June, 1909.

BERNARD D. \VILLIS.

Witnesses:

EDWARD D. FALEs, ARTHUR J. RAY. 

